A material that cross-reacts with antibodies against mammalian insulin, and that has biological activity when tested against mammalian cells, seems to be widespread among protists and bacteria; it has been identified in at least five, representing every such organism in which it has been sought, including Neurospora crassa. Complementing this finding, we have shown several effects of mammalian insulin upon a wall-less strain of N. crassa, including: enhancement changes; stimulation of glucose metabolism; stimulation of growth; morphological changes; stimulation of glucose metabolism: stimulation of glycogen synthesis; activation of the enzyme glycogen synthase, probably by dephosphorylation, as has been reported to occur in mammalian cells. These cells possess specific, high affinity saturable insulin binding sites on their surface, similar to those of mammalian cells, and membrane tyrosine protein kinase activity. We propose to characterize the insulin-insulin receptor diad present in N. crassa. We will clone cDNAs coding for insulin and insulin receptor proteins, selecting from a lambdagt11 library, compare the deduced protein sequences with those of corresponding mammalian proteins. We will purify the insulin receptor from N. crassa membranes, and characterize its protein kinase activity, if any, and prepare antibodies against its constituent polypeptides. We will use clones and antibodies to investigate the function of the insulin-insulin receptor axis in normal fungal growth and development.